Add lib2to3.__main__ to make it easier for debugging purposes to run 2to3.
diff --git a/Tools/scripts/2to3 b/Tools/scripts/2to3
index fbd4aa6..2eb5dad 100755
--- a/Tools/scripts/2to3
+++ b/Tools/scripts/2to3
@@ -1,5 +1,4 @@
 #!/usr/bin/env python
-import sys
-from lib2to3.main import main
+import runpy
 
-sys.exit(main("lib2to3.fixes"))
+runpy.run_module('lib2to3', run_name='__main__', alter_sys=True)